1. Field of the Invention
The present invention relates to a semiconductor manufacturing apparatus, and more particularly, to a wafer stage capable of correcting the flatness of a wafer placed on a chuck using a vacuum suction force and a method employing same.
This application claims priority from Korean Patent Application No. 10-2006-0016465, filed Feb. 20, 2006, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein.
2. Discussion of the Related Art
In general, semiconductor devices are manufactured by repeatedly performing processes such as etching, diffusion, deposition, and photolithography in a selective or sequential manner. The photolithography process mainly includes an application process for applying a photoresist onto a wafer, an exposure process for disposing a reticle in which a circuit pattern is designed on the wafer on which the photoresist is applied and for radiating light onto the wafer. A development process selectively removes the photoresist using a developer by dividing a portion exposed to the light radiated during the exposure process and an unexposed portion.
Here, the apparatus for performing the photolithography process is mainly classified into an application and development apparatus generally called a spinner, and an exposure apparatus generally called a scanner or stepper. The application and development apparatus and the exposure apparatus are in-line linked to perform the photolithography process on the wafer. The exposure apparatus includes a wafer stage on which a wafer is placed. Here, the wafer stage includes a chuck on which the wafer is placed directly by a vacuum suction force applied through a central portion of the chuck. A plurality of protrusions supporting the bottom surface of the wafer is provided on the top surface of the chuck.
Typically, a wafer is placed on the upper side of the chuck while the central portion of the wafer is supported by a lift pin. The bottom surface of the wafer is supported by the protrusions of the chuck while a predetermined vacuum suction force is applied to the bottom surface of the wafer through holes in the central portion of the chuck. The vacuum suction force is applied between the protrusions on the upper side of the chuck. Because the vacuum suction is applied to the central portion of the wafer, this suction force decreases toward the edge of the wafer which allows the edge of the wafer to deflect upward. The inclination of the edge of the wafer increases the step rate at the edge of the wafer. Thus, the focus length becomes short causing a focusing defect and a normal circuit pattern cannot be transferred onto the edge of the wafer increases product defect rates. In addition, the wafer is more stepped toward the edge after the polishing process. When the exposure is performed onto the top surface of the wafer's edge stepped in this manner, a focusing defect may be caused as described above.